1. Field of the Invention
The present invention relates to a circuit module in which a plate-shaped board and a frame-shaped board are bonded together and to a circuit device including the circuit module.
2. Description of the Related Art
Circuit modules having higher packaging densities and a reduced size are described in Japanese Unexamined Patent Application Publication No. 6-216314, Japanese Unexamined Patent Application Publication No. 7-50357, Japanese Unexamined Patent Application Publication No. 2000-101348, and Japanese Unexamined Patent Application Publication No. 2001-339137. In such circuit modules, a plurality of connection electrodes is provided on a surface of a plate-shaped board, such as a ceramic board, and a plurality of connection electrodes, which correspond to the plurality of connection electrodes provided on the surface of the plate-shaped board, is provided on a surface of a frame-shaped board made of resin or other suitable material. The surface of the plate-shaped board faces the surface of the frame-shaped board. The connection electrodes on the plate-shaped board and the connection electrodes on the frame-shaped board are bonded together using conductive bonding materials, such as solder. Circuit components, such as semiconductor elements, are provided on portions of the surface of the plate-shaped board, the portions being located inward relative to the frame-shaped board. A sealing resin is filled in a cavity defined by an inner surface of the frame-shaped board and the surface of the plate-shaped board such that the sealing resin covers the circuit components.
The sealing resin is filled in the cavity to protect the circuit components provided on the plate-shaped board (i.e., to prevent short-circuiting caused by wire deformation when the circuit components are connected to the plate-shaped board by wire bonding and to prevent short-circuiting or other damage caused by foreign matter entering into a space between terminals when a bare chip or a flip chip is used) and to improve the mechanical strength of the circuit module. For the sealing resin, a thermosetting resin, such as an epoxy resin, is commonly used.
When the sealing resin is filled in the cavity and then heat curing is performed, the resin contracts at a specific rate. This contraction stress is also exerted on the frame-shaped board, and a force drawing the frame-shaped board inwardly is generated. The Young's modulus of ceramic is in the range of about 100 GPa to about 300 GPa, whereas, the Young's modulus of resin is in the range of about 10 GPa to about 60 GPa. Thus, although the plate-shaped board, which is a ceramic board, is not substantially deformed, the frame-shaped board made of resin is likely to be deformed. In recent years, a further reduction in the size of a circuit module has been required. Since the width of a frame-shaped board is very small, such as several hundred micrometers, deformation has been more likely to occur. As a result, a problem of inward deformation of the frame-shaped board due to the contraction stress of a sealing resin is likely to occur.